The present invention concerns an apparatus of serially plunge cutting boiler tubular panels or walls. Specifically, the present invention concerns a panel saw for plunge cutting boiler tubular panels formed from a series of parallel tubes joined side by side, and connected by webs usually in a single plane.
Tubular walls formed from a plurality of parallel tubes welded together side by side usually with connecting webs of metal are used in various heat exchanger environments. One such environment is a boiler in a steam driven electrical power generating plant, where the tubes are arranged to form a continuous fluid circuit. Water is run through the tubes and is heated by the burning fuel of the boiler to generate steam which powers electrical turbo generators. The steam generated by the water heated in the boiler tubular walls is used to run electric turbines for generating electricity.
The tube walls of such boilers are generally of such a large scale that should an area of the tube wall become damaged, it is not economically feasible to replace the entire tube wall. Rather, the section of the tube wall which contains the damaged tubes is usually removed and replaced by welding in a new section of tube wall with dimensions that correspond to the dimensions of the removed section of wall.
In accordance with the prior art, the section of the damaged tube wall may be removed manually by using hand held power saws or torches to cut out a rectangular section which includes the damaged tubes by cutting two parallel spaced apart horizontal lines and two parallel spaced apart vertical lines through the tube wall. However, this method of cutting and removing the damaged section of the wall is time consuming and the parallel cuts made by hand-held power tools or torches is often rough and inaccurate, making it difficult to properly dimension a new section of tubular wall to replace the damaged section removed. Moreover, the cut edge is not even and the working conditions for the saw or torch operator make it difficult to be precise.
Other cutting systems are known in the prior art which provide a guide means for panel saws that can be secured directly to the tube wall to provide an accurate cut line. In one such device, a saw is slidably mounted on the guide means for movement therealong. As the saw is moved along the guide means, it cuts a line in the tube wall parallel to the guide means, following which the guide means can then be removed and repositioned to cut additional lines in the wall to enable removal of a section of the damaged tube wall. Because the guide permits a precise straight line to be made, a new section of tube wall can be accurately dimensioned to replace the section of tube wall removed. This type of system is described, for example, in U.S. Pat. No. 4,633,555 granted to G. A. Legge.
However, this apparatus for making a straight cut through the tube wall also has several disadvantages. Because the saw is supported for making a running cut, substantial manual effort is involved in pushing the saw into the panel and along the guide rail to penetrate the panel and make the cut. Should the saw require servicing, the saw must be disassembled from the guide, making servicing the saw difficult and time consuming.
An additional device that is known in the art includes a panel saw for repairing boiler tube walls that is slidably mounted on a guide rail and which pivots in a direction towards and away from the tube wall to make a series of plunge cuts in the wall. This device produces a faster and more precise cut, requires less operator effort, but uses a manually secured brake system to secure the panel saw to the guide way. Such a system is described in U.S. Pat. No. 4,739,688 granted to M. T. Brennan et al.
In this system the brake means must be engaged manually at each cut position and the manually released to move the panel saw to the next cutting position. The additional steps of manually engaging and releasing the brake add to the overall time and effort involved in making the complete straight line cut through the tube wall. In addition, the device of U.S. Pat. No. 4,739,688 includes a complex linkage and lock arrangement for guiding the saw in a plunge cut and for locking the saw against pivotal movement.